This invention relates to a process on a continuous casting machine for the production of strands, in particular of steel strands, in which molten metal is introduced into a tubular mold and is withdrawn from the mold in a partly solidified state. The invention also includes an apparatus for performing the process.
2. Description of the Prior Art
On continuous casting machines of the vertical or curved type, the withdrawal machine is regulated on the basis of a specified strand withdrawal velocity. The direction and speed of the withdrawal will normally remain constant during casting. To maintain the specified conditions and/or to determine anomalies in the guide section of the cast strand or in the mold, the prior art (U.S. Pat. Nos. 3,478,808 and 3,358,743) recommends measuring the current absorbed by the drive unit of the withdrawal machine, and using this value in a control circuit to control or regulate a continuous casting machine. With a constant withdrawal direction and an oscillating mold, this method is intended to yield information on the sliding action of the strand in the mold. The prior art cited above also indicates that other information on the strand produced can be obtained, for example, by measuring the surface temperature of the strand below the mold, by measuring across the thickness of the strand, or even by measuring the length of the strand produced. This information may also be included in the control circuit of the continuous caster.
On horizontal continuous casting machines with oscillating or fixed molds, the withdrawal direction does not necessarily remain constant even though the strand is continuously in motion The strand could be transported in steps with intervening stops or could be transported with a short reverse stroke and another stop.
Depending on the dimensions and withdrawal speed of the strand, there is a distance of several meters between the mold and the drive unit for the strand, since the drive unit is generally located in the vicinity of the completely solidified strand. Between the mold and the drive unit, such as in the vicinity of the solidification section, a portion of the strand is still molten but includes the thin steel shell which is relatively weak at the high temperatures. Moreover, it is known that a reproducible withdrawal rate of the strand is of decisive importance for the formation of the steel shell in the mold and for the achievement of an acceptable strand surface. Because of the mechanical instability or weakness of the partly-molten strand, the methods described above, however, cannot determine whether or not the withdrawal rate specified by the drive unit is transmitted by the strand to the segment of the strand in the mold and, if so, with what effect.